1. Field of the Invention
The present invention relates to a semiconductor laser device. More particularly, the present invention relates to a semiconductor laser device of a double hetero structure.
2. Description of the Prior Arts
Conventional semiconductor laser devices have been of a structure as shown in FIGS. 1 and 2. In such semiconductor laser devices, an active region, where laser is oscillated, in an active layer 24 is limited not only in a vertical direction by a hetero junction between a first upper clad layer 22 and a lower clad layer 26 in FIG. 1 but also in a horizontal direction by providing a current blocking layer 16. That is, an area of a pumping region is decreased by limiting pumping current to a portion where the current blocking layer 16 is not provided (that is, a striped groove 31) to reduce an amount of current required for pumping. With such structure, since an oscillation region is small, a complicated oscillation hardly occurs. Consequently, uniform laser beam is obtained.
When a semiconductor laser device is used for reading out (picking up) bit information with an optical information recording/reproducing apparatus such as a compact disk player, etc., a part of the laser beam oscillated by the semiconductor laser device is reflected by a pick up optical system (including the disk) and returned to the semiconductor laser device itself. It is known that oscillation of the semiconductor laser device is affected by the optical feed back since the above semiconductor laser device has coherence so that noise is generated in the outputted laser beam. Such noise causes a reading-out error in such optical information recording/reproducing apparatus.